a. Field of the Invention
The present invention relates to an electronic three-phase four-wire system watt-hour meter suited for the precision measurement of the electric energy of a three-phase four-wire system A.C. load.
B. Prior Art
Measurement of the electric energy of three-phase four-wire system A.C. loads, in general, requires three watt-hour meters or three electric energy measuring elements. Conventional three-phase four-wire system watt-hour meters consist of three operational circuits each of which multiplies the voltage and the current of one phase and converter circuits which convert the currents of the operational circuits into voltages. The outputs of the three current-voltage converter circuits are converted into a frequency signal by a voltage-frequency converter circuit, and the electric energy of a three-phase system is displayed by a pulse counter.
Conventional watt-hour meters of the above type require a lot of electronic parts and have deficiencies with regard to reliability and manufacturing cost. Furthermore, non-matching characteristics of the operational circuits and current-voltage converter circuits create interphase imbalance errors, thereby necessitating the provision of error adjusting means and rendering the assembling operations clumsy and troublesome. Besides, they impose limitations on measuring accuracy.